The present invention relates to a light emitting device, for example, including a light source, and a color conversion layer which converts a color of light from the light source, a display device using the light emitting device, and a color conversion sheet.
From the past, a liquid crystal display (LCD; Liquid Crystal Display) has been used as a thin display device. A backlight irradiating the whole surface of a liquid crystal panel from behind is utilized in the liquid crystal display, and the liquid crystal display is roughly classified into the direct method and the edge light method, depending on the structure thereof. In the edge light system, surface emission is performed on the top face of a light guide plate by allowing light to enter from the side face of the light guide plate, and propagate inside the light guide plate. Also, in the direct system, the surface emission is performed by arranging a plurality of fluorescent lamps in parallel in the same plane. Today, the display has been progressively grown in size, and the direct method has become the mainstream for uniformly illuminating the whole panel having the large area with high luminance (for example, refer to Patent literature 1).
Meanwhile, in recent years, a backlight using a light emitting diode (LED: Light Emitting Diode) has attracted attention so as to realize further reduction in thickness and weight, long service life, and reduction in an environmental damage of the large display, and also from the viewpoint of improvement of moving image characteristics by blinking control. The following two methods are able to be used for irradiating white light to the panel with the backlight using such an LED.
In the first method, as illustrated in FIG. 21(A), LEDs 100R, 100B, and 100G having three colors of red (R: Red), blue (B: Blue) and green (G: Green) are used, and the white light is synthesized by simultaneously lighting these LEDs 100R, 100B, and 100G. On the other hand, in the second method, the blue LED is used as a light source, and a phosphor layer partly converting a color of light emitted from this blue LED is provided, and thereby the converted color light and blue light are mixed to emit the white light. For example, as illustrated in FIG. 21(B), the second method is realized by providing a flat-plate shaped phosphor layer 101 separately from the plurality of blue LEDs 100B which are arranged in the same plane. Alternatively, as illustrated in FIG. 21(C), the second method is realized by forming a phosphor layer 103 so as to cover a light emitting section 102 in the blue LED 100B in which the light emitting section 102 is connected to a cathode frame 105a and an anode frame 105b with a wire bond 104, and which is entirely sealed by an outer cap 107.
For example, in the case where a GaN blue LED chip is used as the above-described phosphor layer, epoxy resin, silicon resin, or the like in which a YAG phosphor is mixed is used. Thereby, the blue light from the blue LED chip is partly converted into yellow color light in the phosphor layer, and it is possible to obtain the white light as a whole (for example, refer to Patent literature 2). However, since the light emission spectrum is wide in the above-described YAG phosphor, in the case where the YAG phosphor is used for a backlight for a liquid crystal display, matching with a liquid crystal color filter is poor, and a color gamut is narrowed. Thus, by adding phosphors of other colors, such as red, or green and red, to the YAG phosphor, the color gamut is expanded, and the color reproducibility is improved.
However, since such a phosphor layer is sensitive to water vapor in air, and is deteriorated by being subjected to the water vapor, it is not possible to obtain a desirable light emission chromaticity and a desirable light emission efficiency.
Thus, the method in which the phosphor layer is formed on the face inside the outer cap of the blue LED chip, and the inside of the cap is evacuated, or filled with an inert gas atmosphere for hermetic sealing has been proposed (Patent literature 3). Also, the method in which the phosphor layer is sandwiched and sealed by two glass substrates has been proposed (Patent literature 4).